The objectives of this project are (1) to assess psychophysical method of experimental pain measurement; (2) to assess clinical pain measures in a dental setting; (3) to determine the validity of experimental pain models by comparison of experimental and clinical pain responses; and (4) to evaluate known pharmacological and non-pharmacological pain-control agents. The interactive computer-based staircase scaling method was used in five experiments. The first experiment, performed in dental patients immediately before an oral surgical procedure, showed that the staircase method successfully tracks the time course of both the analgesia produced by narcotic infusion and the reversal of this analgesia by administration of a narctic antagonist. The method also showed hyperalgesia following antagonist administration in comparison to placebo, suggesting sensitivity to endogenous opioids released in anticipation of oral surgery. The second experiment assessed time course of 1.1 ug/kg fentanyl analgesia following infusion rates of 2, 5, 10 and 20 min to evaluate the model's potential for detecting opioid analgesia enhancement by potentiating agents. Analgesia was rate dependent and rates of 10-20 mins appear ideal for agonist evaluations. The third experiment assessed the influence of the serotonergic agonist MCPP on pain sensitivity in pain-free subjects. MCPP had no apparent effect, a result consistent with another study in this laboratory in which MCPP did reduce pain associated with postherpetic neuralgia. The fourth experiment investigated if the absence of cardiac chest pain during "silent ischemia" may represent a natural analgesic state detectable by experimental methods. Preliminary results suggest that patients with silent ischemia show normal sensitivity to thermal pain sensations. The fifth study assessed if two weeks treatment with the narcotic antagonist naltrexone increases opiate sensitivity. The results of three initial cases show no effect which may represent premature assessment after naltrexone termination resulting in residual opiate antagonism. A new computerized version of the DDS scale was tested in pain-free subjects. The method is used more easily and provides increased range and less bias effects than the previous paper and pencil version.